1. Field of the Invention
This invention relates to a wet-process apparatus and a control method for the same and, in particular, to a wet-process apparatus which is equipped with a function of quickly creating a highly clean space as needed when using chemicals in a clean room, and to a control method for such an apparatus.
2. Description of the Related Art
FIG. 4 is a schematic sectional view of a conventional wet-process apparatus. In the drawing, a wet-process apparatus 1 includes a chamber 2 isolated from the atmospheric air. Provided in the upper section of the chamber 2 is a nitrogen-gas supply pipe 3 for supplying nitrogen gas 4 into the wet-process apparatus 1. The nitrogen gas 4 introduced into the wet-process apparatus 1 through the nitrogen-gas supply pipe 3 is fed to a fine cleaning filter 6 by means of a nitrogen-gas supply fan 5 to become highly clean nitrogen gas 7, which is introduced into a working space 9 separated from atmospheric air by an opening/closing means 8, such as a window or a door that can be opened and closed.
Arranged in the working space 9 is a chemical vessel 11 containing a chemical 10, and, lodged in the chemical vessel 11 are a plurality of semiconductor wafers 13 held by a cassette 12, which can be immersed in and taken out of the chemical vessel 11, and further, transferred to other places, by means of an automatic transfer handle 14. The chemical vessel 11 is supported by a draining board 15 having a large number of holes to allow waste liquid 16 of the chemical 10 to drop therethrough. The waste liquid 16 is discharged through a drain port 17 provided at the bottom of the apparatus.
When the highly clean nitrogen gas 7 is contaminated with mist of the chemical 10, it becomes contaminated nitrogen gas 18, which is discharged to the outside through a gas outlet 19.
An example of such a wet-process clean apparatus for creating a highly clean space as needed when using chemicals in a clean room, is disclosed, for example, in Japanese Patent Laid-Open No. 2-211216.
In the conventional wet-process apparatus 1, constructed as described above, the nitrogen gas 4 supplied through the nitrogen-gas supply pipe 3 is conveyed to the fine cleaning filter 6 by the nitrogen-gas supply fan 5, supplying the working space 9 with highly clean nitrogen gas 7. In the working space 9, the highly clean nitrogen gas 7 flows downwards from above, creating a highly clean nitrogen-gas atmosphere in the space. Further, in this space, the automatic transfer handle 4 carries out the operations of immersing or extracting the cassette 12, containing semiconductor wafers 13, in or out of the chemical 10 and transferring it to some other place.
Insofar as they are transferred through the nitrogen-gas atmosphere, the semiconductor wafers 13 which have been processed with the chemical 10 are free from the formation of a natural oxide film thereon; however, if transferred through air which contains oxygen and water, the wafers cannot avoid the formation of a natural oxide film thereon, adversely affecting the characteristics of the semiconductor devices to be made of these wafers. Accordingly, it is desirable that the wet-process operation be performed in a highly clean nitrogen-gas atmosphere.
On the downstream side of the working space 9, the highly clean nitrogen gas 7 is contaminated with mist of the chemical 10, and is discharged through the gas outlet 19 to the exterior of the system as contaminated nitrogen gas 18. Further, that portion of the chemical 10 which has flowed downwards through the draining board 15, accumulates in the lower section of the wet-process apparatus as waste liquid 16, which is discharged through the drain port 17 to the exterior of the system.
A problem with the conventional wet-process apparatus 1, described above, is that all the nitrogen gas 3 supplied thereto is discharged to the exterior of the system, which means a large quantity of nitrogen gas is required to maintain a nitrogen-gas atmosphere in the working space 9 for a long period of time, resulting in an enormous running cost for the apparatus.